Wiktionaryβ

all mouth and trousers

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mouth, meaning "talk" rather than action and trousers, presumably at the time of origin a reference to masculinity, either as trousers as a male item of clothing, or a reference to the genitals, being for some reason required in order for effective action to be taken. In the context of the time of origin it was perhaps a somewhat sexist term. The phrase originated in Northern England citation needed